"That was the game changer for me," says Moses. "That gave me a really good reason for doing it – it wasn't like Love Island where you go on and sell your soul."

He immediately had a charity in mind. For the last four years, Sol3 Mio have been involved with an organisation called Dream Chaser Foundation, which supports children with cancer and their families.

"They do incredible things, and they don't get a lot of publicity, so I wanted to help them out if I could," tells Moses.

Moses says Sol3 Mio's Pene (middle) and Amitai encouraged him to give the show a go.

Once he'd agreed to do the show, Moses says he panicked when he realised he had very little time to try to get fit.

"I'd just finished doing Sol3 Mio's Back to Basics tour and I'd spent a lot of time watching videos until 4am after shows, so I wasn't in great shape. I got a week's trial at the local gym and went at it like a maniac. I was there for five days straight and on the sixth day, I couldn't move."

He also relished being part of a team that had to work closely together.

"I don't function as well as a solo player; I am in my element in a small group who are looking out for each other. I think that's why I love being part of Sol3 Mio and it was the same being in Mako team."

While there were moments when the competitiveness was intense, and there was one person he was keen to see the back of – "I'm not telling who!" he grins – that wasn't the toughest part of being on Celebrity Treasure Island either.

"For me, the hardest thing was when they filmed us answering questions about what was going on and talking about how it made us feel. I could tell they were after drama and that's not me – if there is an issue, I try to find a solution and move forward while avoiding any drama."

Moses in his element.

Moses says he struggled with the interviews to start with.

"You haven't eaten and you haven't slept, and your brain isn't really working, and they're trying to make it dramatic, and they're asking you things like, 'Who is the weakest link?' I found that hard, I didn't want to say something negative about somebody when I didn't actually feel that way. But you had to answer the questions and I would walk away thinking, 'What did I just say?'

"Then I had a revelation. I decided if they wanted drama, I would choose three things that had happened each day that had affected me and work out what I wanted to say in advance, and that way I wouldn't be stumbling over my words."

Moses devised strategies to cope with the demands of reality television – including getting up well before the cameras arrived!

Being prepared about what to say, rather than being put on the spot with the questions, made the interviews easier, says Moses.

Similarly, he developed a strategy for dealing with having cameras around so much.

"It felt really intrusive to start with, so I coped by thinking of every day as a performance. When I am singing, I get up in the morning knowing it's performance day. I get my suit ready, I know what I will be eating and how I will navigate the day. It was the same on Treasure Island, only I was washing my Crocs instead of getting my suit ready.

"I woke up super-early and Gary Freeman and I would go down to the beach and have a yarn about life for a couple of hours before everyone else got up. It was a good way to step out of the game for a bit and to prepare, and by the time the cameras turned up, I would be ready for showtime."

The opera star says he got into the swing of island life easily. Supplied

Another tactic that helped with the pressure of reality TV was singing.

"It kept me going," he admits.

"Nobody had any music because we weren't allowed phones, but I am used to entertaining myself with my singing. Unfortunately, I got told off by the powers that be because I sang all the time and they have to pay for the rights to use the songs on TV. So they'd be saying, 'Moses, stop singing!'"

While there were tricky times, he enjoyed the experience.

"I'm glad I did it. I feel like I learned a lot. My character was tested, but that's good.

"One thing that has come out of it is that I've made close friendships. Our camp became like family. They called us the kumbaya camp because nothing fazed us. We would lose a challenge and say, 'Oh well, it's just a game. We'll find our feet again.' The other team was really competitive, and they didn't like that."

While he doesn't think of himself as a celebrity – "Everyone must have been going, 'Who is that guy?'" – he's pleased to have had the chance to use the public profile he has for a good cause.

"That was what it was all about for me. I love what I do with Sol3 Mio and my other singing, and if I can also do things like raise money for Dream Chaser and help to put these guys on the map, then I'm very happy."

The important work Moses' chosen charity Dream Chaser Foundation does

Ryan and Keri are delighted Moses is competing for their charity on Celebrity Treasure Island.

Keri and Ryan Topperwien are usually far too busy to watch television, but they're making an exception for Celebrity Treasure Island.

That's because their Dream Chaser Foundation is Moses Mackay's chosen charity, and he's going all-out to win as much money for them as possible.

"We're just thrilled," says Keri (35), adding they're delighted that he's not only helping with raising funds, but also awareness of what they do.

"Being selected for such a high-profile television series is amazing for us. We are a grassroots charity, we do everything ourselves. To be selected is so cool and we can't thank Moses enough."

The foundation, which supports children with cancer and their families, was set up in memory of their son Chace, who died of acute myeloid leukaemia in 2012, aged three.

"After Chace died, we were left with this complete emptiness, trying to figure out what to do next," says Keri.

"We didn't have any other children at the time and we were at a loss. When you have done everything you can to save your child and it has failed, you start thinking, What is the point? You go to some pretty dark places.

"We dealt with it by trying to help other parents going through the same thing, and the charity sprang up pretty soon after."

Dream Chaser Foundation provides practical and financial support to families who have a child with cancer, helping with everything from petrol and grocery vouchers, through to donations towards funeral costs.

"When your child is diagnosed with cancer your life gets paused and one or both parents has to stop work," says Keri, who is an environmental consultant.

"The bills mount up and you still have your usual responsibilities.

"We had to take a mortgage holiday and we were lucky to have really good support but it is still really tough."

Adds Ryan (35), who works in a cardboard mill, "We felt there was a real need for practical support. There are other charities that send kids with cancer and their families on holiday to the Gold Coast and that's awesome, but when they get home they might not be able to afford to pay the power bill or for petrol to get to the hospital."

The fundraising they do helps families to pay for these kinds of expenses.

They have a programme called Dream Chaser guardians, in which people can sign up to donate as little as $1 a week. Keri and Ryan recently gave $95,000 raised from the guardian scheme to sponsor a room for the family of a child with cancer at Ronald McDonald House in Auckland for the next 10 years.

Another big part of the Dream Chaser Foundation is its bone marrow drive, aimed at encouraging people to sign up as potential donors for New Zealand's bone marrow registry, particularly those of Maori and Pacific Island ancestry.

When Chace was diagnosed with his rare and aggressive form of leukaemia, his parents were told his best chance of surviving was to have a bone marrow transplant. But because of his Maori heritage, there was only a tiny pool of potential donors, and none of them was a suitable match.

"When we were told that, it was devastating," says Ryan. "A bone marrow transplant was our silver bullet, then we found out it wasn't possible because there were no matches for our son."

Keri adds, "Other kids on the ward who needed transplants would have their information put into the data base and get pings back saying there were multiple matches. I thought we would be lucky like everyone else, but when you are in an ethnic minority group, your chances plummet."

Today, out of 34 million people on the worldwide bone marrow registry, only 9000 have Maori or Pacific Island ancestry, hence Keri and Ryan's push to get more people to sign up.

Moses and fellow Sol3 Mio members Pene and Amitai have all signed up, and they also promote Dream Chaser whenever they can.

Keri and Ryan are grateful for the support – as well as running the foundation, the Bay of Plenty couple are working full-time and raising two kids, Chace's siblings Zayn (5) and Evie (2).

"We are pretty much on the go all the time, and that's not going to change – there is always going to be a need for what we're doing," tells Keri.

"We're committed to doing this, in Chace's memory, for the rest of our lives, and we're thankful for any help we get."